G. H. Park 



arker 



the full force of these rays yet without any apparently disastrous 

 effects. 



If a colony of Stylotella in natural position in quiet, clear sea- 

 water is closely examined, its numerous oscula, which occupy 

 either the tips of the fingers or slignt elevations on the surface of 

 its body, will be found as a rule to be widely open, so that an 

 observer can look far down into the interior of the animal and see 

 much of the branched gastral cavity and the excurrent canals 

 leading into it. Although the fingers of the sponge are generally 

 not much over seven to eight millimeters in diameter, the oscula 

 may measure as much as four and a half millimeters in width when 

 fully expanded thus giving a considerable view of the internal 

 cavities. If such a colony is suddenly lifted out of theseawater 

 into the air, the water rapidly drains from it and the air rushes 

 through its oscula into its internal chambers. On returning such 

 a sponge to the sea, the air thus introduced is with diflSculty dis- 

 lodged and may eventually as large bubbles distort and deform 

 the sponge. Sponges that are exposed to the air on the beach by 

 the natural fall of the tide show no such inclusions of air, and an 

 examination of them in seawater brings to light the fact thattheir 

 oscula are all firmly closed thus preventing the entrance of air. 

 The steps of this closure can be easily followed by watching a 

 sponge that is gradually becoming exposed to air when, in a quiet 

 sea, the tide is falling. Under such circumstance the oscula 

 remain open till they come into direct contact with the air when, 

 with about three minutes, they close. If now the sponge colony 

 IS moved into deeper water, theoscula will reopen in from seven 

 to ten minutes. If oscula at different levels on the same sponge 

 are watched, those that come in contact with the air first, close 

 first and those that are situated at a deeper level do not close until 

 they in turn have been exposed to the air. These conditions are 

 easily reproduced in the laboratory. Thus if a colony of fresh 

 sponge is carried into the laboratory and placed in a glass vessel 

 in which a current of seawater in kept running, on exposing the 

 tip of any finger to air its osculum will close in a few minutes to 

 reopen after it has been reimmersed in seawater for about ten 

 minutes. On quickly removing a sponge from the sea the chim- 



